The invention relates to the preparation of alkyl tert alkyl ethers and, particularly, to a process for preparing alkyl tert alkyl ethers from liquid olefinic hydrocarbon feedstock containing sulfur and to an ion exchange resin for use in the process.
Alkyl tert alkyl ethers such as methyl t-butyl ether (MTBE) ethyl t-amyl ether (TAME) ethyl t-butyl ether (ETBE) and the like are used as fuel extenders and octane value improving agents to produce unleaded gasoline having acceptable octane values without varying the compounding ratio of the gasoline.
Alkyl tert alkyl ether additives serve as substitutes for lead anti-knock compounds. Because lead anti-knock compounds yield undesirable emissions from the exhaust gas of a combustion engine, substitution of additives according to the invention provides reduced environmental pollution.
Alkyl tert alkyl ethers are typically produced by reacting a primary alcohol with an olefin having a double bond on a tertiary carbon atom. For example, methanol can be reacted with isobutylene to form methyl t-butyl ether (MTBE), and with isopentene to form methyl t-amyl ether (TAME). Ethanol, as another example, can be reacted with isobutylene to form ethel t-butyl ether (ETBE).
The reaction to form alkyl tert alkyl ethers is catalyzed by Lewis acids such as sulfuric acid, and organic acids such as alkyl and aryl sulfonic acids and ion exchange resins. Ion exchange resins in acid form are particularly useful, and macroporous cation exchange resins doped with or otherwise containing hydrogenation metals of groups VI, VII and VIII provide good results.
However, typical feedstocks for the reaction such as light hydrocarbon streams from FCC operations have been found to rapidly deactivate the resin during etherification, thereby making the process inefficient and costly. Examples of known processes for preparing alkyl tert alkyl ethers are disclosed in U.S. Pat. No. 4,330,679 to Kohler et al., U.S. Pat. No. 4,695,556 to Oeckl et al., U.S. Pat. No. 5,008,466 to Schleppinghoff et al. and U.S. Pat. No. 5,084,070 to Kohler et al.
However, none of the foregoing patents provides a process which addresses the problem of rapid ion exchange resin deactivation.
It is therefore the principal object of the invention to provide a process for preparing alkyl tert alkyl ethers wherein the ion exchange resin is not rapidly deactivated.
It is another object of the invention to provide a process for etherification of a light hydrocarbon stream wherein a high quality raffinate byproduct is provided for downstream use in alkylation processes.
It is still another object of the invention to provide an ion exchange resin for use in preparation of alkyl tert alkyl ethers wherein the resin is resistant to deactivation.
Other objects and advantages will appear hereinbelow.